1. Technical Field
The present invention relates to a vehicle body structure for a fuel cell vehicle, and more particularly, to a vehicle body of a fuel cell vehicle including a lower vehicle body structure of an upper body for reinforcing a floor kick-up portion.
2. Background Art
Vehicle industry has rapidly grown centering on gasoline and diesel internal combustion engines for more than one hundred years, but it is now confronted by a tremendous change due to problems such as environmental regulations, threat to energy security and exhaustion of fossil fuel.
Many developed countries have entered into competition of developing future vehicles with environment-friendly, high efficient and high-tech features, and major vehicle companies are trying to survive in such keen competition.
In accordance with the demand of the times for environment-friendly products which can resolve a fossil fuel exhaustion problem, vehicle companies have been actively developing electric vehicles which use an electric motor as a power source.
In this connection, research on a vehicle with a fuel cell system mounted thereon has been actively undergone.
As well known, a vehicle with a fuel cell system supplies hydrogen to a fuel cell stack as fuel to generate electric energy which is used to operate an electric motor to drive a vehicle.
Here, a fuel cell system is a sort of a power generating system which does not change chemical energy in fuel to heat by combustion but electrochemically generates electric energy therein.
A fuel cell system comprises a fuel cell stack for generating electric energy, a fuel supplying system for supplying fuel (hydrogen) to the fuel cell stack, an air supplying system for supplying oxygen in the air as an oxidizer used in an electrochemical reaction, and a heat/water management system for externally discharging reaction heat of the fuel cell stack and controlling a driving temperature of the fuel cell stack.
In such a fuel cell system, electric energy is generated by an electrochemical reaction of hydrogen as fuel and oxygen in the air, generating heat and water as a reaction byproduct.
As a fuel cell system, a proton exchange membrane fuel cell (PEMFC) is widely used due to high output density.
Meanwhile, a conventional fuel vehicle has a vehicle body of a box-type structure called “a monocoque body” which does not have a frame.
The monocoque body is configured by a combination of thin panels and reinforcing members to provide an engine room, a passenger room and a trunk room and is designed to distribute an external force caused in the event of a vehicle crash to the whole body.
In the conventional vehicle body structure, a humidifier for humidifying air supplied to a fuel cell stack, the fuel cell stack for generating electric energy by an electrochemical reaction between hydrogen as fuel and oxygen in the air, and a fuel processing system for controlling pressure of hydrogen supplied from a hydrogen tank to supply hydrogen as fuel are mounted in an engine room of a monocoque body, whereas a plurality of hydrogen tanks are mounted below a rear floor of a monocoque body.
The humidifier and the fuel cell stack mounted in a fuel cell vehicle are very heavy in weight.
If these heavy parts are mounted in the engine room of the monocoque body, a monocoque body configured by combining very thin panels which are mold-manufactured may not endure the strength and, so the monocoque body may become very weak in durability for enduring an external force. That is, providing the monocoque body with sufficient strength requires its structure to be more complicated.
In order to resolve the above problems, as shown in FIG. 1, a vehicle body structure which comprises an upper body 100 and a chassis frame 200 as a dedicated platform for a fuel cell vehicle has been suggested.
The upper body 100 is configured by combining thin panels and reinforcing members to provide an engine room, a passenger room, and a trunk room. The upper body 100 comprises a roof 101, a filler 102, a fender 103, a hood 104, a trunk lid (not shown), a dash panel (not shown), a center floor 105, and a rear floor 106 which are made by molding thin panels, like the monocoque body of an internal combustion engine.
The chassis frame 200 comprises a plurality of longitudinal members and a plurality of transverse members. The chassis frame 200 includes two side members 210 as longitudinal members. It also includes a plurality of cross members 222 and 223 as transverse members, which are arranged between the side members 210 and bumper reinforcing members 231 and 232.
That is, the chassis frame 200 for forming a lower portion of the vehicle body is arranged to apply a frame body of the fuel cell vehicle and forms a vehicle body of the fuel cell vehicle together with the upper body 100. In the chassis frame 200, main fuel cell system parts such as a humidifier 11, a fuel cell stack 12, a FPS 13, and a hydrogen tank 14 are mounted.
The chassis frame 200 is provided with a plurality of body mounting portions 217a to 217d. The upper body 100 is to be coupled to the chassis frame 200 through the body mounting portions 217a to 217d. 
Referring to FIG. 1, provided are eight body mounting portions 217a to 217d for mounting the upper body onto the chassis frame 200. The body mounting portions 217a to 217d of the chassis frame 200 are located at positions where corresponding portions of the bottom of the upper body 100 exist. The upper body 100 is coupled to the chassis frame 200 at the eight positions.
Since the upper body 100 is coupled to the chassis frame 200 only through the body mounting portions 217a to 217d, the body mounting portions 217a to 217d of the chassis frame 200 serve to transfer load applied to the upper body 100.
Meanwhile, hydrogen which is fuel of a fuel cell vehicle is stored in a hydrogen tank 14 in a gas state, and two or three hydrogen tanks are installed before or after a rear suspension.
Since hydrogen is stored in a gas state, the size of each hydrogen tank is increased, which interferes with setting a ground clearance and securing a passenger room.
As shown in FIG. 2, a floor kick-up portion 107 must exist at a connection portion between the center floor 105 and the rear floor 106 of the upper body 100 due to the hydrogen tank 14 installed below the vehicle body.
A center floor side of the floor kick-up portion 107 is a portion which is coupled to the body mounting portion (217c in FIG. 1) of the chassis frame 200, and the body mounting portion 217c must exist at a corresponding location of the chassis frame 200 in order to couple the upper body 100 and the chassis frame 200.
In a fuel cell vehicle dedicated platform, the floor kick-up portion 107 of the upper body 100 is a portion on which passengers sit and below which the hydrogen tank 14 is located. The floor kick-up portion 107 is a very important portion to provide the passengers with ride comport and protect not only passengers but also the hydrogen tank 14 from a vehicle crash including side crash.
In case of gasoline and diesel vehicles, there is no possibility that a fuel tank is destroyed in a side crash. In case of the fuel cell vehicle having hydrogen tank, however, it is expected that the side crash badly affects the fuel cell system due to a layout of the fuel system and the size of the hydrogen tank.
Therefore, for fuel cell vehicles, there is a need for an improved vehicle body structure for protecting the fuel system from a side crash, which can minimize transformation of the vehicle body in the event of a vehicle crash and maximize protection of passengers and hydrogen tank.
Also, since the floor kick-up portion of the upper body is a location where the concentrated load is transferred from the body mounting portion of the chassis frame, there is a urgent need for a vehicle body structure for efficiently distributing or dispersing the concentrated load and preventing vibration and transformation due to the load.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.